As women have entered the workforce in increasing numbers, researchers from a variety of disciplines have considered the likely consequences on the health of their children. The direction and magnitudes of the effects of maternal labor supply on various dimensions of child health are theoretically ambiguous. Maternal labor supply provides income and may supply access to employer-provided health insurance for her family. However, it also places an additional burden on a mother's time and may result in the poorer supervision or care of her children. My research seeks to identify the effect of maternal labor supply on the health of school age children in the United States. The problem is made difficult by the simultaneous nature of the work and child health decisions. A mother's choice to participate in the formal labor market is endogenous and is generally considered to be the effect of, not the cause of, her family's characteristics. Mothers with healthy children may find it easier to work, whereas mothers of children with special needs may find working outside of their home difficult. Similarly, having a child with a chronic condition may make it necessary for a mother to work in order to provide health insurance or additional income for her family. Isolating the effect of a mother's labor force participation on the health of her children is confounded by this reverse relationship: a child's health may directly affect a mother's labor supply decision. To estimate the causal relationship from maternal labor supply to child health, this project utilizes quasiexperimental [unreadable] variation in maternal labor supply generated by the interaction between the age composition of [unreadable] the children in the household and the age when children can start school. To be specific, the opportunity cost of a woman's time is substantially lowered when her youngest child becomes eligible for public school, leading to an increase in maternal labor supply at that time. In a two-stage regression model, this project uses a mother's youngest child's eligibility for kindergarten as an instrument for maternal labor supply. This research will provide the best estimate to date of the causal effect of maternal labor supply on the health of school-age children. This project will yield an important contribution to the understanding of the public health burden, if any, due to increasing maternal labor supply. Children's health is not only important for its own sake, but poor child health also imposes costs to families and society. Policies aimed at mitigating the strain on working mothers and that help women combine work and family life should be supported and informed by good, quantitative research on the impacts of maternal labor supply on children. [unreadable] [unreadable] [unreadable]